The role of lymphangiogenesis in promoting metastasis via the lymphatic system has been the subject of extensive research. Vascular endothelial growth factor receptor-3 (VEGFR-3) is a major mediator of lymphangiogenesis. VEGF-C and VEGF-D are two ligands for VEGFR-3. Both of them were shown to stimulate lymphangiogenesis in transgenic mice. Specifically, three cancer cell lines transfected with VEGF-C or VEGF-D were recently reported to exhibit increased tumor lymphangiogenesis and undergo lymphatic metastasis. Clinical studies also revealed that increased expression of VEGF-C was associated with lymph node metastasis in a variety of cancers in human. Thus, it is desirable to develop novel drugs that inhibit VEGFR-3 activities for use in treating cancer.